1. Field of the Invention
The present invention is directed to fuel injectors of the type which include a check valve packaged in the lower nozzle assembly for fuel supply backflow-preventing purposes and a timing check valve packaged in the upper barrel assembly for timing fluid supply backflow-preventing purposes. In particular, to such fuel injectors which are of the unit fuel injector type which operate on the time-pressure metering basis.
2. Description of Related Art
U.S. Pat. No. 4,971,016 issued to Peters, et al. relates to a closed loop fuel supply system for high pressure fuel injectors providing precise and independent pressure control of both fuel and timing fluid on a pressure-time (P-T) basis. However, this control is achieved by pilot pressure controlled servo valves in supply passages leading to the injector and not by way of precision check valves positioned in the barrel of the injector itself.
The use of check valves for preventing the back flow of fluid in a fluid control system is known in a wide variety of arts as reflected, e.g., by U.S. Pat. Nos. 3,053,459; 3,374,502; 3,394,888; 3,685,739; and 5,056,488. Furthermore, the use of conventional ball type check valves to prevent back flow of fuel from injection and metering chambers is shown, for example, in U.S. Pat. No. 5,040,511 to Eckert. However, while Eckert provides a check valve in supply lines to the injection and metering chambers, these check valves play no part in the process of metering fuel into these chambers, the check valve merely being opened by the pressurized fuel supplied to the injector and remaining open until the entire amount of previously metered fuel is passed into the respective chamber.
In injection systems as disclosed by Eckert and others, the amount of fuel or timing fluid directed to the timing fluid chamber or injection chamber of a unit injector is controlled by metering systems which supply the respective chamber with a metered amount of fluid. This requires elaborate metering systems, e.g., wherein the fuel is passed through a metering orifice prior to its passage to the fuel injector itself. Consequently, numerous elements are required in order to pass the requisite amount of fuel to the unit fuel injector.
Furthermore, with conventional check valves, the spring and free floating ball tend to be unstable at certain flow ranges. That is, at certain engine speeds, fuel passing through the check valve causes the ball element to vibrate laterally within the check valve thus inducing unstable fuel flow and thus a significant variation in the flow of fuel through the valve. With today's high pressure unit injectors, it is essential that a stable and consistent check valve be provided so as to ensure that the metering of fuel to the injector be both consistent and uninterrupted to meet the stringent accuracy requirements.